Well-aligned TiO2 Nanotube Arrays Research Articles

Improved Sensitivity and Selectivity of Glutathione Detection through Target-Driven Electron Donor Generation in Photoelectrochemical Electrodes.

Glutathione (GSH) plays a vital role in many physiological processes, and its abnormal levels have been found to be associated with several diseases. In contrast to traditional methods using electron donor-containing electrolytes for photoelectrochemical (PEC) sensing, in this study, a target-driven electron donor generation in a PEC electrode was developed to detect GSH. Using well-aligned TiO2 nanotube arrays (TNTs) as the PEC substrate, mesoporous MIL-125(Ti) was grown in the TNTs through an in situ solvothermal method and subsequent two-step annealing treatment. The accommodation capacity of mesoporous MIL-125(Ti) allows a well loading of cystine and Pt nanoclusters (NCs). Taking advantage of the specific cleavage ability of disulfide bonds by GSH, cystine was converted to cysteine, which served as the electron donor for the PEC process. Benefiting from the confinement effect of mesoporous MIL-125(Ti), cysteine was effectively oxidized to cysteine sulfinic acid by the photogenerated holes. Importantly, the highly active Pt NCs decorated in the mesopores not only improved the charge transfer but also accelerated the above oxidation reaction. The synergistic effect of these factors enabled the efficient separation of the photogenerated electron-hole pairs, which induced a significant photocurrent increase and in turn led to the high-sensitivity detection of GSH. Consequently, the proposed PEC biosensor exhibited excellent performance in the detection of GSH in serum specimens. The target-driven electron donor generation designed in this study might open a new route for developing sensitive and selective PEC biosensors with application in complex biological environments.

Preparation of Well-Aligned TiO₂ Nanotubes with High Length-Diameter Aspect Ratio by Anodic Oxidation Method.

This paper focused on the influence of various oxidation parameters such as electrolyte composition, reaction time, calcination temperature and current change on the morphology and structure of TiO2 nanotube arrays. It was found that ammonium fluoride with a high viscosity reduced the diffusion rate of fluoride ions and significantly increased the length of TiO2 nanotubes, creating nanotubes with ordered arrays and uniform diameters. Meanwhile, the time of anodic oxidation determined the length of TiO2 nanotube arrays. Well-aligned nanotube arrays could be obtained after 0.5-2.5 h of oxidation. In addition, when the oxidation temperature was about 30 °C, the TiO2 nanotube arrays achieved the optimal uniformity and the maximum length-diameter aspect ratio. The morphology and quality of the TiO2 nanotubes fabricated were estimated through current as a function of reaction time. Consequently, formation mechanism of TiO2 nanotube arrays was investigated undergoing three major periods. The findings of this study can shed some light on the optimal conditions for preparing well-aligned TiO2 nanotube arrays with high length-diameter aspect ratio.

Electrochemical reduction and capacitance of hybrid titanium dioxides—nanotube arrays and “nanograss”

In this paper, we report enhanced electrochemical capacitance of well-aligned TiO2 nanotube arrays with “nanograss” synthesized by electrochemical anodization. The conductivity of hybrid materials is improved by electrochemical reduction method, exhibiting an outstanding specific capacitance of 14.3mFcm−2, which is 14 times larger than pristine ones. The specific capacitance further increases up to 20.5mFcm−2, which is 43.4% higher than reduced ones with selectively retention of “nanograss” by ultrasonic treatment. We expect that the electrochemical-reduction approach and controllable morphology modification offer a potential path for developing high-performance energy storage devices.

Fabrication of Well-Aligned TiO2 Nanotube Arrays with Outstanding Light-Induced Hydrophilicity Performance

TiO2 nanotube arrays (TiO2-NTAs) were respectively fabricated using traditional one-step oxidation and re-oxidation method on a titanium surface in fluorine-containing electrolytes. Microstructures, optical properties of specimen were characterized by X-ray diffractometer, digital microscope, field-emission scanning electron microscope and ultraviolet-visible spectroscope. Compared with the one-step oxidation, the resulted samples showed more uniform surface, longer tube length and statistical higher absorption in visible light region. Importantly, a new growth mechanism named template-induced growth model is proposed to explain the growth of TiO2-NTAs prepared by re-oxidation approach in present work. Besides, water contact angles of samples before and after irradiated by UV light were measured and discussed in detail. It is confirmed that samples obtained from re-oxidation method have more hydroxyl groups can be formed when irradiated by UV light, which lead to more sensitive light-induced hydrophilicity finally. The light-induced hydrophilic performance of TiO2-NTAs would be favorable to improve the likelihood of electrolyte contacting of the surface, which is useful in many realistic application instances.

Visible-light-driven photoelectrochemical and photocatalytic performances of Cr-doped SrTiO3/TiO2 heterostructured nanotube arrays

Well-aligned TiO2 nanotube arrays have become of increasing significance because of their unique highly ordered array structure, high specific surface area, unidirectional charge transfer and transportation features. However, their poor visible light utilization as well as the high recombination rate of photoexcited electron-hole pairs greatly limited their practical applications. Herein, we demonstrate the fabrication of visible-light-responsive heterostructured Cr-doped SrTiO3/TiO2 nanotube arrays by a simple hydrothermal method, which facilitate efficient charge separation and thus improve the photoelectrochemical as well as photocatalytic performances.

Enhanced photocatalytic activity from Gd, La codoped TiO2 nanotube array photocatalysts under visible-light irradiation

Well-aligned TiO2 nanotube arrays were successfully synthesized from electrochemically anodic oxidation, which were further codoped by Gd and La via hydrothermal and sol–gel methods. The visible-light photocatalytic activities of the Gd, La codoped TiO2 nanotube arrays evaluated by photodegrading methyl orange (MO) have been significantly enhanced compared to that of undoped TiO2. Hereinto, the photocatalytic performance of Gd, La codoped TiO2 nanotube array synthesized by a hydrothermal approach was better than that by a sol–gel method. A lower band gap energy was attributed to the enhanced response to visible light. The new concept was helpful to guide the synthesis of robust visible-light photocatalysts, and the interesting results suggested that the Gd, La codoped TiO2 nanotube arrays were very promising for elevated the solar utilization in environment management.

Photoelectrochemical properties of TiO2 nanotube arrays: effect of electrolyte pH and annealing temperature

The effect of electrolyte pH and annealing temperature on the formation of TiO2 nanotube arrays in connection with the photoelectrochemical response was investigated in this article. Well-aligned TiO2 nanotube arrays were fabricated by anodisation of Ti foil in an electrolyte consisting of 1 M of glycerol (85 wt% of glycerol and 15 wt% of water) with 0.5 wt% of NH4F at 30 V for 30 min. The pH of the electrolyte was varied from pH 1 to 7. With the increase of electrolyte pH to neutral condition, the length of the nanotube arrays was increased from ∼320 to 1100 nm. As-anodised TiO2 nanotube arrays were amorphous in nature. However, anatase phase was observed after annealing at 400°C and polycrystalline anatase and rutile phase could be observed by heating up to 500°C in air atmosphere. Based on the results obtained, the length and crystalline phases of TiO2 nanotube arrays affect the performance of photoelectrochemical response and photoconversion efficiency significantly.

Investigation on the Photoelectrocatalytic Activity of Well-Aligned TiO2Nanotube Arrays

Well-aligned TiO2nanotube arrays were fabricated by anodizing Ti foil in viscous F−containing organic electrolytes, and the crystal structure and morphology of the TiO2nanotube array were characterized and analyzed by XRD, SEM, and TEM, respectively. The photocatalytic activity of the TiO2nanotube arrays was evaluated in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of methylene blue (MB) dye in different supporting solutions. The excellent performance of ca. 97% for color removal was reached after 90 min in the PEC process compared to that of PC process which indicates that a certain external potential bias favors the promotion of the electrode reaction rate on TiO2nanotube array when it is under illumination. In addition, it is found that PEC process conducted in supporting solutions with low pH and containing Cl−is also beneficial to accelerate the degradation rate of MB.

Electrochemical Properties of Highly Ordered TiO<sub>2</sub> Nanotube Arrays as an Anode Material for Lithium-Ion Batteries

Well-aligned TiO2 nanotube arrays were fabricated from anodization by a subsequent heat treatment. Rate performance and electrochemical properties of TiO2 nanotube arrays were studied intensively. The electrode exhibits excellent rate capabilities at various rates with an average coulombic efficiency reaching 95.6%. It is obvious that TiO2 nanotube array possesses high rate capability and excellent cycling stability.

Influence of the organic electrolyte and anodization conditions on the preparation of well-aligned TiO2 nanotube arrays in dye-sensitized solar cells

► Dye-sensitized solar cells (DSSCs) were fabricated using well ordered TiO 2 nanotubes . ► Nanotubes were prepared by electrochemical etching of Ti foil in fluorinated organic solvents . ► Using NH 4 F-EG as an anodizing electrolyte, longer nanotube length of 18 μm was achieved. ► NH 4 F-EG system showed higher energy conversion efficiency ( η = 2.13%) than HF-DMSO system ( η = 1.16%). ► We conclude that the lower efficiency may be due to the lower dye adsorption surface area. Dye-sensitized solar cells (DSSCs) comprising randomly networked titanium nanoparticles usually exhibit lower energy conversion efficiency and limited electron mobility due to the scattering and trapping of free electrons. In this study, attempts were made to improve the electron mobility in DSSCs using vertically aligned and well ordered TiO 2 nanotubes. These nanotubes were prepared by the electrochemical etching of Ti foil under potentiostatic conditions in four different fluorinated organic solvents under varying anodizing conditions like reaction time, and annealing before/after anodization. Sonoelectrochemistry was found to be more effective to synthesize well-ordered TiO 2 nanotubes than just stirring the electrolyte as in conventional electrochemistry. Using NH 4 F-EG as an anodizing electrolyte, unique TiO 2 nanomorphology with longer nanotubes length of 18 μm was achieved. The photo-electrochemical properties of the DSSCs with back illumination under UV (<400 nm) and simulated sunlight (AM 1.5) were also studied, and exhibited an efficiency of 2.13%. The results are reported in detail here.

Fabrication of open-ended TiO2 nanotube arrays by anodizing a thermally evaporated Ti/Au bilayer film

Fabrication of TiO2 nanotube arrays (TNAs) with through-hole morphology is practical significance to enhance the photocatalytic activity of TNAs, as well as expanding their applications. In present work, open-ended TNAs are synthesized on a conductive Au layer by anodizing a thermally evaporated Ti/Au bilayer film. In the anodizing process, the upper Ti layer is transformed into well-aligned TNAs. The barrier layer under the growing TNAs ultimately touches the Au layer and is completely dissolved by the electrochemical etching. In order to avoid the bubble disruption of TNAs caused by the water electrolysis after the Au layer is exposed to the electrolyte, a specific non-aqueous electrolyte is used. The XRD results reveal that the as-formed open-ended TNAs are amorphous and can be transformed into anatase by annealing at 350°C.